Clip the end of the gun onto the zerks, it will kinda pop onto them. Then pump the gun, you will hear the old grease popping and squeezing it's way out as it is forced out. I pump mine 10 times or so until nothing but new fresh red grease is coming out everywhere. Then you have to pull on the hose from the grease gun to get it to come off.
Then for the fun part you get to take your finger and scrape all the old grease out of the joints and wipe it on a paper towel or so. This keeps it from slinging around and making a huge mess. Grease all the zerks. For the slip joints on the front and rear shaft I usually just pump them until I see a slight bit of movement in them. These won't squeeze out, they will just keep filling and filling and expanding the joint.
Then go for a drive with 4WD drive engaged, you'll be fine on pavement since you have multimode. This should sling any excess that you didn't get out off. You'll probably smell a slight burning smell from where some of it gets slung up on the muffler.
Hope this helps.